1. Field of the Invention
The present invention relates to a digital rights management (DRM) and, in particular, to a DRM method and DRM-enabled portable device for controlling playbacks of DRM contents on the basis of content usage log.
2. Description of the Related Art
Digital Rights Management (DRM) is an access control technologies to protect the intellectual property of the distributed digital media by limiting usage of digital media using encryption techniques. That is, DRM technology allows securely transmitting content from a Content Provider (CP) to a user and protecting the contents from being illegally used and distributed.
DRM technologies attempt to control the digital content through all the phases of creation, distribution, use, abrogation; and access to protect rights of the owner of the digital content in online and even offline states.
In order to use a DRM content item on a mobile device, a user accesses a content server providing DRM content and downloads the DRM content item together with its metadata and license using the mobile device. Here, the metadata contains information regarding the DRM content item and the license contains information regarding a key for decrypting the encrypted DRM content item and associated usage right (e.g., amount of usage time and period).
After downloading the DRM content item and its metadata and license, the user can use the DRM content item in the usage range specified in the license.
Conventionally, the license associated with a DRM content item is updated when it is completely played. For example, if a DRM content item having a license allowing up to 100 times of playback is completely played once, the license on the DRM content item is updated such that the valid playback times of the DRM content item is decreased by 1 to become 99. However, the conventional license update mechanism has a drawback in that the license update fails when the currently playing DRM content item is abnormally stopped, e.g. by battery power shortage, whereby this vulnerable characteristic is likely to be used malevolently.